const_constructor_param_type_mismatch

A value of type '{0}' can't be assigned to a parameter of type '{1}' in a const constructor.

The analyzer produces this diagnostic when the runtime type of a constant value can't be assigned to the static type of a constant constructor's parameter.

The following code produces this diagnostic because the runtime type of i is int, which can't be assigned to the static type of s:

class C {
  final String s;

  const C(this.s);
}

const dynamic i = 0;

void f() {
  const C(i);
}

Pass a value of the correct type to the constructor:

class C {
  final String s;

  const C(this.s);
}

const dynamic i = 0;

void f() {
  const C('$i');
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.0. Page last updated on 2025-05-08. View source or report an issue.